Polypropylene resin has a good processing property, anti-medicament property, chemical resistance, weather resistance and electrical performance. Thus polypropylene resin is usually used in a broad range of technical fields including auto parts, electric appliances and office automation equipment, as well as all kinds of injection molded articles, blow molded articles, vacuum or pressed air molded articles, film or sheet. Among these fields, the polypropylene resin used in the field of interior parts of a car can also be used in the fields where a higher balance of physical properties such as stiffness and a high-impact property are required, by adding polypropylene with a filler or a rubber.
Recently, polypropylene resin used in the field of interior parts of a car is required to have an enhanced impact strength. In order to enhance impact strength, the molecular weight of polypropylene moiety or rubber moiety has been increased. However, by increasing such a molecular weight, flowability of a melted resin is reduced when polypropylene resin composition is injection molded, in particular when a large injection molded article such as an instrument panel or a bumper is molded. Accordingly, there is a problem in which a flow mark or weldline appears on the surface of the obtained article to devalue the article. Although a defective portion can be covered by a mat painting on the whole of or part (flow marked or weldlined part) of the article, a cost increase would be inevitable. Therefore, requests for a material in which the above-mentioned problem does not occur and which does not need to be painted is increasing rapidly.
Recently, in interior parts of a car such as an instrument panel, in particular an article with embossed pattern, lower gloss material is also required in order to provide lived-in-feeling and inhibition of reflectance of sunlight to improve safety.
However, one defect of lower gloss articles is that the articles are easily scratched when such articles contact each other when the articles are being carried, when the articles come in contact with clothes such as work gloves while assembling parts, or when the articles come in contact with a metal such as that of a buckle of a seat belt. Another defect of such articles is that any scratch thereon is usually outstanding because of the lower gloss. Such problem with respect to scratching is especially remarkable in the unpainted article as mentioned above.
As for a method for improving the appearance of a molded article by preventing the aforesaid weldline and a method for obtaining lower glossing, a method for using a crystalline ethylene-propylene copolymer characterized by its molecular weight distribution and relaxation time has been known [please see, for example, Japanese Patent Unexamined Published Applications (hereinafter referred to as “J.P. KOKAI”) Nos. 9-71714 and 9-71619]. As for a method for improving the appearance of a molded article by preventing the aforesaid flow mark and a method for obtaining a uniform gloss, a method for using an ethylene-propylene copolymer characterized in obtaining a melting viscosity at a specific frequency has been proposed (J.P. KOKAI No. 9-328526).
Furthermore, as for improvement of scratch resistance, a technique for adding a specific polyethylene (J.P. KOKAI No. 57-73034), a technique for using a filler having a specific particle size (J.P. KOKAI No. 57-8235) and a technique for reducing a frictional coefficient and increasing the hardness of the surface of a molded article by adding a high crystalline polyethylene with a lubricant such as a fatty acid amide to improve its scratch resistance (J.P. KOKAI No. 2001-288331) have been known.
However, while these known methods and polypropylene resin compositions obtained therefrom somewhat improve the appearance and the scratch resistance property of a molded article, they are not sufficient for using on interior parts of a car. Especially, considering that the requirements for interior parts of a car are that it has both a low gloss and a good physical balance, it is seen that these known methods and polypropylene resin compositions obtained therefrom can not meet such requirements sufficiently.